The present invention relates to a light-emitting device, a method for manufacturing the light-emitting device, and an electronic apparatus including the light-emitting device.
In recent years, flat-panel displays which have low power consumption and which are lightweight have been demanded since various information apparatuses incorporating the displays have been developed. An organic electroluminescent device including light-emitting layers is known as an example of such flat-panel displays. In the organic electroluminescent device, the light-emitting layers are usually arranged between a cathode and anodes. In order to enhance the hole injection efficiency and/or electron injection efficiency, the following organic electroluminescent devices have been disclosed: an organic electroluminescent device including hole injection layers arranged between anodes and light-emitting layers, an organic electroluminescent device including electron injection layers arranged between light-emitting layers and a cathode, and other organic electroluminescent devices.
Most of materials for forming light-emitting layers, hole injection layers, and electron injection layers included in organic electroluminescent devices are usually deteriorated by the reaction with moisture in air. If these layers are deteriorated, non-luminescent regions referred to as dark spots are caused in the organic electroluminescent devices. This leads to a reduction in life. In the organic electroluminescent devices, it is a challenge to prevent damage caused by moisture, oxygen, or the like.
In order to meet the challenge, the following technique has been usually used: a technique in which a sealing member made of glass or metal is joined to a substrate included in an organic electroluminescent device such that moisture and/or oxygen is prevented from penetrating the device. However, in large-screen displays having low thickness and weight, it is difficult to prevent the penetration of moisture and/or oxygen using only sealing members. Since such large-screen displays need to have an area sufficient to arrange driving elements and wires, a top-emission structure in which light is emitted through a sealing member has been disclosed. In order to cope with such a requirement, a sealing structure including a transparent, lightweight thin-film with high strength has been demanded.
In order to cope with large-screen flat displays, a technique referred to as thin-film passivation has been recently disclosed in, for example, JP-A-9-185994 (hereinafter referred to as Patent Document 1), JP-A-2001-284041 (hereinafter referred to as Patent Document 2), JP-A-2000-223264 (hereinafter referred to as Patent Document 3), and JP-A-2003-17244 (hereinafter referred to as Patent Document 4). In this technique, a thin-film serving as a gas barrier layer is formed over light-emitting elements by a high-density plasma deposition process such as an ion-plating process, an ECR plasma-enhanced sputtering process, an ECR plasma-enhanced CVD process, a microwave plasma-enhanced CVD process, or an ICP-CVD process using a transparent ceramic material, such as silicon nitride or silicon dioxide, having good gas barrier properties. This technique is effective in preventing moisture from penetrating the light-emitting elements.
However, even if this technique is used, the penetration of external moisture cannot be completely prevented; hence, sufficient luminescent properties and life cannot be achieved. In particular, steps present around the gas barrier layer or present on partitions for partitioning pixels are easily chipped or cracked and moisture penetrates the chipped or cracked steps.
The gas barrier layer can probably be prevented from being cracked in such a manner that an organic buffer layer of which the upper face is substantially flat is provided under the gas barrier layer. This is because the organic buffer layer can absorb the stress due to the warpage or volume expansion of a substrate. Since the upper face of the organic buffer layer is substantially flat, the gas barrier layer disposed on the upper face thereof is substantially flat; hence, the gas barrier layer has no stress-concentrated portion. This prevents the cracking of the gas barrier layer.
However, if the organic buffer layer is thermally distorted (expanded or shrunk), the gas barrier layer is cracked. Therefore, there is a problem in that the penetration of external moisture cannot be completely prevented.